Emulsion explosives are well-known in the art. See, for example, U.S. Pat. Nos. 4,356,044; 4,322,258; 4,141,767; 3,447,978 and 3,161,551. Emulsion explosives comprising an emulsion phase blended with ammonium nitrate (AN) prills and/or ANFO prills also are well-known in the art. See, for example, U.S. Pat. Nos. 4,294,633 and 3,161,551.
An inherent problem with emulsion explosives, however, and particularly with emulsion and prill mixtures, is their relative instability, due to the fact that they comprise a thermodynamically unstable dispersion of supercooled solution or melt droplets in an oil-continuous phase. If the emulsion remains stable, the supercooled droplets are prevented from crystallizing or solidifying into a lower energy state. If the emulsion weakens or becomes unstable, however, then crystallization or solidification of the droplets results, and the explosive generally loses at least some of its sensitivity to detonation and becomes too viscous to handle for certain blasting applications. Moreover, when solid components are added to emulsion explosives, such as glass microspheres for density reduction or prills or particles of oxidizer salt or ANFO for increased energy, such solid components tend to destabilize emulsions even further. The solid components may disrupt the continuous fuel phase and provide a site for resulting crystallization of the discontinuous oxidizer salt solution phase. In addition, the prills often contain fines and/or a clay or talc coating that act as poisons to the emulsion thereby hastening its destabilization. Since emulsion and prill combinations must remain stable during handling and for a period of time after being loaded into a borehole in order to remain reliably detonable, the presence of AN or ANFO prills can present serious stability problems.
It has been found in the present invention that if the liquid fuel component of the ANFO prills contains a dissolved surfactant of the types hereafter described, or if such a surfactant is added to AN prills, the stability of the resulting emulsion and AN or ANFO prills mixture is greatly enhanced over a similar mixture not containing a surfactant so dissolved in the fuel portion or added to the AN prills. For optimum performance, the selection of a surfactant can be based on the type of AN prill and coatings involved as well as the type of emulsifier system used.